The subject invention finds particular utility in the heavy duty truck and trailer industry. In this industry, the use of air brakes and air-ride beam-type suspensions has become quite popular. Such suspensions come in wide and varied forms. Generally speaking, however, they include a pair of longitudinally extending beams (flexible or rigid) one of which is located adjacent each of the two longitudinal side frame rails located underneath the body of the truck or trailer. These beams are then pivotally connected at one end to the frame hanger that is attached to the frame rail of the vehicle. Spaced along the remaining length of the beam is an air bag (bellows) and an axle. The beam may be underslung or overslung, with respect to the axle, and the air bag(s) may be located fore or aft of, or in a vertical line with, the axle. The axle may be connected to the beam rigidly or resiliently. The beam may extend in a "trailing" or a "leading" direction from its pivot, thus defining a trailing or leading beam suspension. Equivalents of air bellows, such as large rubber balls or pads or hydraulic cylinders, may be employed instead of air bags.
Prior to the advent of the invention in U.S. Pat. No. 4,166,640, the truck and trailer suspension art had not been able to successfully achieve a rigid axle-to-beam connection employing a rigid beam. In short, either the axle-to-beam connection had to be made, in some way, resilient, and/or the beam had to be made flexible, in order to successfully take up the operative articulation forces experienced during vehicle operation, even though a resilient bushing was employed at the pivotal connection (e.g. in the hanger bracket) between the beam and frame rail. By employing a sufficiently sized, resilient pivotal connection which provided a greater degree of deflection, hangerwise than beamwise, thereby to take up the operative forces at the pivot while tracking and roll-stability were maintained, the invention disclosed in the above-cited '640 patent (see FIGS. 5, 6 & 8) constituted a significant, indeed pioneer, advance in the truck and trailer suspension field. This pioneer advance occurred because, by the use of such a unique pivotal connection, there could then be used in combination with this resilient pivotal connection a rigid beam and a rigid axle-to-beam connection. In fact, in the preferred forms of this patented invention, the resilient pivotal bushing system was so designed that it took up, successfully, virtually all of the operative articulation forces during vehicle use, while the suspension as a whole meets all criteria for a very safe suspension. In addition, maintenance requirements were significantly reduced and life-expectancy dramatically increased over known suspensions employing resilient axle-to-beam connections, while at the same time, the extra weight of attendant resilient beams (e.g. leaf springs) was avoided. In some instances, in fact, the resilient bushings at the pivot outlasts the life of the vehicle.
In 1991, an important improvement in the aforesaid invention was disclosed, upon the issuance of U.S. Pat. No. 5,037,126. Employing the basic concepts in the '640 patent of a rigid axle-to-beam connection, rigid beam, and orificed resilient pivot bushing, the invention of the '126 patent included a unique rigid beam and axle connection thereto which significantly reduced the weight of the overall suspension even further.
The above two patented suspensions are ideal examples of rigid beam, trailing arm suspensions finding high acceptability in the truck and trailer industry. The pioneer inventive concept of U.S. Pat. No. 4,166,640 in this respect constitutes the preferred background from which the instant invention arises.
Examples of other resiliently bushed axle-to-beam connection suspensions employing rigid beams may be found, for example, in U.S. Pat. Nos. 3,332,701; 3,140,880; 3,482,854; 3,547,215; and 3,751,066. Examples of flexible beam-type suspensions with resilient or rigid axle-to-beam connections include U.S. Pat. Nos. 3,785,673; 3,918,738; 3,612,572, as well as the GMC Astro-Air suspension, the Dayton Air Suspension, Western Unit Air Suspensions, Hutchens Suspensions, and the Fruehauf Cargo Care and Pro-Par Suspensions, just to name a few.
Generally speaking, in trailing and leading beam-type suspensions, a rather unique problem occurs. The problem is that during operation of the vehicle, the axle may be stressed to a cross-sectional shape other than as manufactured (e.g. stressed "out-of-round", if a cylindrical axle is employed). There are two different loading conditions that cause this unique problem:
1. forces imposed on the suspension and axle during vehicle cornerings; and PA1 2. forces imposed on the suspension during a vertical single-wheel input.
Referring to FIGS. 1 and 2, a rear view of a typical trailer, adequately illustrates these forces. Trailer 1 is formed of body 3, wheels 5, axle 7, and side frame rails 9 (the suspension is omitted for clarity).
FIG. 1 shows the forces incurred during trailer cornering. CG is the center of gravity of the vehicle. As trailer 1 is maneuvered about a corner, a centrifugal force "F" acts upon the vehicle at its center of gravity CG. The force "F" is proportional to the radius of the curve, or corner, and the vehicle's speed squared. This creates a roll moment "M" that is proportional to the height of the center of gravity off the ground and the magnitude of centrifugal force "F". Since the vehicle is in a steady state condition, the roll moment is resisted at the tire-to-road interface by an equal but opposite moment created by unloading the tire of one side of the vehicle by a force "W" and increasing the load on the opposite side tire by the same force magnitude "W".
The roll moment causes the trailer to lean as depicted in FIG. 1, and is due to tire and suspension deflections. The tire deflection is proportional to "W" and the radial spring rate of the tires. The suspension deflection is proportional to force "F", the effective roll center of the suspension, and the roll rate of the suspension.
The forces caused by this roll moment must be transferred from the vehicle body, through the suspension into the axle and on through the tires to the road surface. Transferring the loads from the suspension into the axle is much different in leading and trailing arm air suspensions than in any other type of suspension, thereby creating the previously mentioned unique problem of leading and trailing arm air suspension systems.
FIG. 2 illustrates the same trailer 1 and load configuration as in FIG. 1, except the axle, tires and part of the suspension are omitted. Elements 11 in the drawing are the hanger brackets that attach the suspension to the body of the trailer. In this case, the roll moment "M" is resisted by equal but opposite forces "S" that the suspension inputs to brackets 11. The forces "S" are similar for virtually all recognized types of suspensions. The forces "S" for brackets 11 are, of course, the same for any such suspension employed with brackets 11 (as generically illustrated).
Reference now is made to FIG. 3. FIG. 3 illustrates one side of a typical spring suspension 13 that consists of front suspension bracket 21, rear suspension bracket 22, steel spring 23, means 24 for attaching spring 23 to axle 7, and radius rod 26. The force "S", as depicted in FIG. 2, is distributed between the two suspension brackets 21 and 22, onto both ends of spring 23, then transferred through spring/axle attachment 24, and into axle 7. The resultant force transferred into axle 7 is simply the vertical force "S.sub.v ". If the other side of this type of suspension were shown, the loading would be the same except the vertical force would be in the opposite direction.
Another known type of suspension is illustrated in FIG. 4. Here, half of a typical walking beam suspension 15 consists of front suspension bracket 31, rear suspension bracket 32, steel spring 33, and saddle assembly 34 that pivotally attaches spring 33 to walking beam 35. Axle brackets 36 pivotally attach beam 35 to axles 7A and 7B. The force "S", as depicted in FIG. 2, is distributed between the two suspension brackets 31 and 32, onto both ends of spring 33, then transferred through saddle assembly 34 and into walking beam 35. The force is then transferred equally to axles 7A and 7B. The resultant force transferred into each of axles 7A and 7B is simply half the vertical force "S" (here illustrated as S/2). If the other side of this type of suspension were shown, the loading would be the same except vertical force "S" would be in the opposite direction.
Most known suspensions behave in the manner as those depicted in FIGS. 3 and 4, in that the forces put into the suspension to resist roll moment "M" result in forces into the axle that are vertical in nature only. The exception to this, however, is leading and trailing arm air suspensions, wherein an additional force acts upon the axle.
A typical trailing arm suspension 17 is shown in FIGS. 5,6 & 8 in this respect. It consists of suspension bracket 41 which is pivotally attached at 46 to a trailing arm beam 42 that is supported at one end by bracket 41 and at the other end by air spring 43. Beam 42 has a means of a rigid attachment 44 to axle 7. Suspension 17 further includes a typical brake actuation mechanism 19, comprising brake chamber 27, rod 29 and S-cam assembly 37, S-cam bearing 37A and slack adjuster 45. With this design, air spring 43 is designed to have a very low spring rate (i.e. force/deflection), and, therefore, it contributes very little to resisting roll moment "M". The force "S", as depicted in FIG. 2, is transferred primarily into suspension bracket 41 and then into one end of trailing arm beam 42, through rigid axle connection 44 and into axle 7. The resultant forces into axle 7 are a vertical force equal to "S" and a torsional force "T", equal to vertical force "S" multiplied by beam length "L" (i.e. T=S.times.L).
Additionally, the axle acts as a beam element supporting the vertical loads transmitted from the tires through the axle and suspension to the vehicle frame. These loads generate a bending moment into the axle, thereby placing the bottom of the axle in tension and the top of the axle in compression. A weld on the surface in tension creates the potential for an axle life reducing stress riser.
Reference is now made to FIG. 6 which illustrates the complete trailing arm suspension 17 with wheels 5 and axle 7 attached (brake actuation mechanism 19 shown in FIG. 5 is omitted).
FIG. 6 illustrates axle 7 with trailing arm beams 42 attached to and their resultant forces on axle 7. The vertical load "S" is similar for all suspensions, but this type of leading or trailing arm suspension 17 adds an additional torsional force "T" to the axle. It is this torsional force that creates a unique design stress problem that must be overcome in the design of the trailing, or leading, arm suspensions.
While the suspensions disclosed in U.S. Pat. Nos. 4,166,640 and 5,037,126 successfully overcame this unique problem, the instant invention overcomes it in a unique and highly advantageous way, thereby constituting a still further improvement on the basic pioneer invention of the '640 patent. In this respect it should be remembered, as illustrated in FIG. 7, that the forces imposed on a suspension and, therefore, the axle, are the same for single wheel input (e.g. one dual wheel going over a curb "C", as illustrated, or one dual wheel dropping into a pothole), as they are for the case of trailer cornering, as described above with respect to FIGS. 1-6.
FIG. 5 illustrates an embodiment of the invention disclosed and claimed in above-referenced U.S. Pat. No. 5,037,126. In this suspension, and as is widely used in the prior art, U-bolts 39 are used to share in transferring torsional loads "T" caused by the trailing arm suspension into the axle. In '126, furthermore, a rigid, welded axle-to-beam connection is also used. Relatively thick axles are employed, and through proper engineering design, the axle safely accepts torsional loads "T". Nevertheless, U-bolts or similar parts are necessary, and the axle must be designed to be strong (e.g. heavy) enough to accept these forces.
It has now been discovered that virtually all previous commercially acceptable designs of leading or trailing beam suspensions, whether of the '126 or other types as exemplified by citation above, through their design which allows the axle to have transferred to it torsional loads "T", also causes the axle to change its circumferential (i.e. cross-sectional) shape (e.g. "out-of-round" if the axle is cylindrical, as illustrated in FIGS. 5-6). This is caused by inputting torsional loads at two points "M" and "N" (FIG. 5) only around the axle circumference. The U-bolts employed in previous preferred designs serve the function of significantly minimizing this change in cross-sectional shape. Not to do so could otherwise cause unacceptable stress risers at the point of constraint (e.g. at the weld of the axle to the beam). Thus, in most acceptable, known designs of the trailing or leading beam type, U-bolts become a preferred means for improving the life of the suspension and axle.
In view of the above, there exists a considerable, and long-felt need for a new trailing or leading beam suspension which achieves all of the benefits of prior designs of this type, but which also overcomes the need to employ U-bolts, while at the same time not giving rise to stress risers at the axle-to-beam connection, due to torsion and bending forces. It is a purpose of this invention to fulfill this need in the art.
Another problem in the suspension art, which existed and is now overcome by the instant invention should be discussed. The problem experienced, as partially illustrated in FIG. 5, and best illustrated in FIG. 8, was the need in prior suspensions of the leading and trailing beam type to have to attach brake actuation mechanism 19 by bracketry (e.g. 47 and 51) to the axle. Usually this necessitated welding (e.g. 49 and 53) both brake chamber brackets 51 and S-cam bearing brackets 47 by way of six bracket attachments to the axle in an area of high torsional stress. This can result at times in reduced axle life. For this reason, there exists yet another considerable and long-felt need in the art for a new suspension that would allow the safe attachment of the brake actuation mechanism to a part of the suspension other than the axle. It is a further purpose of this invention to fulfill this need in the art, as well as other needs as will become apparent to the skilled artisan, once given the following disclosure.